Silica-reinforced rubber compounded with an organosilane tetrasulfide silica coupling agent at high mixing temperature

Abstract

Sulfur-vulcanizable elastomeric compounds and pneumatic tire components having improved tensile mechanical and dynamic viscoelastic properties are produced by compounding polymers with silica at a temperature of 165° C. to about 200° C., in the presence of a silica dispersing agent, and a very small amount (e.g., about 0.01% to about 1% by weight, based on the weight of the silica) of a bis(trialkoxysilylorgano) tetrasulfide silica coupling agent.

We claim:  
     
       1. A sulfur-vulcanized elastomeric compound produced by a process comprising the steps of: 
       (a) mixing together at a temperature of 165° C. to about 200° C. in the absence of cure agents, an elastomer optionally having an alkoxysilane terminal group, a reinforcing filler comprising silica or a mixture thereof with carbon black, about 0.01% to about 1% by weight, based on the weight of the silica, of a bis(trikoxysilylorgano) tetrasulfide silica coupling agent, and a silica dispersing aid;  
       (b) allowing the mixture to cool below the mixing temperature;  
       (c) mixing the mixture obtained in step (b), at a temperature lower than a vulcanization temperature, with a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure; and  
       (d) curing the mixture obtained in step (c).  
     
     
       2. The compound of  claim 1 , wherein the bis(trialkoxysilylorgano) tetrasulfide silica coupling agent is bis(3-triethoxysilylpropyl) tetrasulfide. 
     
     
       3. The compound of  claim 1 , wherein the bis(trialkoxysilylorgano) tetrasulfide silica coupling agent is present in an amount of about 0.05% to about 1% by weight, based on the weight of the silica. 
     
     
       4. The compound of  claim 3 , wherein the bis(trialkoxysilylorgano) tetrasulfide silica coupling agent is present in an amount of about 0.1% to about 1% by weight, based on the weight of the silica. 
     
     
       5. The compound of  claim 1 , wherein the silica dispersing aid is selected from the group consisting of an alkyl alkoxysilane, a fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, a polyoxyethylene derivative of a fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar, an ester of a polyol, and mixtures thereof. 
     
     
       6. The compound of  claim 5 , wherein the alkyl alkoxysilane has the formula 
       
         
             R   1   p Si(OR 2 ) 4−p    
         
       
       wherein the alkoxy groups are the same or different from each other, each R 1  independently comprises C 1  to about C 20  aliphatic, about C 5  to about C 20  cycloaliphatic, or C 6  to about C 20  aromatic, each R 2  independently comprises C 1  to about C 6 , aliphotic and p is an integer from 1 to 3.  
     
     
       7. The compound of  claim 5 , wherein the alkyl alkoxysilane is a triethoxysilane. 
     
     
       8. The compound of  claim 5 , wherein the alkyl alkoxysilane is present in an amount of about 0.1% to about 25% by weight, based on the weight of the silica. 
     
     
       9. The compound of  claim 8 , wherein the alkyl alkoxysilane is present in an amount of about 0.1% to about 15% by weight, based on the weight of the silica. 
     
     
       10. The compound of  claim 5 , wherein the fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar is selected from the group consisting of sorbitan monooleate, sorbitan dioleate, sorbitan trioleate, sorbitan sesquioleate, sorbitan laurate, sorbitan palmitate, sorbitan stearate, and mixtures thereof. 
     
     
       11. The compound of  claim 5 , wherein the fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar is present in an amount of about 0.1% to about 25% by weight, based on the weight of the silica. 
     
     
       12. The compound of  claim 5 , wherein the polyoxyethylene derivative of the fatty acid ester of a hydrogenated or non-hydrogenated C 5  or C 6  sugar is present in an amount of about 0.1% to about 25% by weight, based on the weight of the silica. 
     
     
       13. The compound of  claim 1 , wherein the diene elastomer is selected from the group consisting of homopolymers of conjugated diene monomers, and copolymers and terpolymers of the conjugated diene monomers with monovinyl aromatic monomers and trienes. 
     
     
       14. The compound of  claim 1 , wherein the diene elastomer is selected from the group consisting of polyisoprene, polystyrene, polybutadiene, butadiene-isoprene copolymer, butadiene-isoprene-styrene terpolymer, isoprene-styrene copolymer, and styrene-butadiene copolymer. 
     
     
       15. A pneumatic tire comprising a component produced from a sulfur-vulcanized elastomeric compound, wherein the compound comprises an elastomer optionally having an alkoxysilane terminal group, a reinforcing filler comprising silica or a mixture thereof with carbon black, about 0.01% to about 1% by weight of a bis(trialkoxysilylorgano) tetrasulfide silica coupling agent based on the weight of the silica, a silica dispersing aid, and a cure agent comprising an effective amount of sulfur to achieve a satisfactory cure, 
       wherein the compound is formed by mixing together the elastomer, the silica, the silica coupling agent and the silica dispersing aid, in the absence of the cure agent, at a temperature of 165° C. to about 200° C., wherein the compound exhibits about a 10% to about a 50% decrease in filler flocculation after compounding, as measured by ΔG′, or reduced hysteresis as measured by about a 5% to about a 20% decrease in tangent δ at 65° C., compared to a similar compound in which a conventional amount of the bis(trialkoxysilylorgano) tetrasulfide silica coupling agent is mixed with the silica, in the absence of the cure agent, at a temperature of 160° C. or less.  
     
     
       16. The tire of  claim 15 , wherein the elastomer is selected from the group consisting of homopolymers of conjugated diene monomers, and copolymers and terpolymers of the conjugated diene monomers with monovinyl aromatic monomers and trienes. 
     
     
       17. The tire of  claim 15 , wherein the elastomer is selected from the group consisting of polyisoprene, polystyrene, polybutadiene, butadiene-isoprene copolymer, butadiene-isoprene-styrene terpolymer, isoprene-styrene copolymer, and styrene-butadiene copolymer. 
     
     
       18. A method for preparing a sulfur-vulcanized elastomeric compound, comprising the steps of: 
       (a) mixing together at a temperature of 165° C. to about 200° C. in the absence of added sulfur and cure agents, an elastomer optionally having an alkoxysilane terminal group, a reinforcing filler comprising silica or a mixture thereof with carbon black, about 0.01% to about 1% by weight of a bis(trialkoxysilylorgano) tetrasulfide silica coupling agent, based on the weight of the silica, and a silica dispersing aid;  
       (b) allowing the mixture to cool below the mixing temperature;  
       (c) mixing the mixture obtained in step (b), at a temperature lower than a vulcanization temperature, with a cure agent and an effective amount of sulfur to achieve a satisfactory cure; and  
       (d) curing the mixture obtained in step (c).  
     
     
       19. The method of  claim 18 , wherein the mixing temperature in step (a) is about 170° C. to about 200° C. 
     
     
       20. The method of  claim 18 , wherein the mixing temperature in step (a) is about 170° C. to about 185° C.